As soon as the parachute was separated from the balloon, the latter ascended with great rapidity, and, being of an oval form, turned itself with a longer axis into an horizontal position.
We now come to the practice of the art. The shape of the balloon is one of the first objects of consideration. As a sphere ad mits the greatest capacity under the least surface, the spherical figure, or that which approaches nearest to it, has been gene rally preferred. However, since bodies of this form oppose a greater surface to the air, and consevently a greater ob struction to the action of the oar or wings than those of some other form, and there fore cannot be so well guided in a calm, or in a course different from the direction of thc wind, it has been proposed to con struct balloons of a conical or oblong figure, and to make them proceed with their narrow end forward. Next to the shape, it is necessary to consider the stuff that is most proper for forming the enve lope of the inflammable or rarefied air. Silk stuff, especially that which is called lutestring, properly varnished, has been most commonly used for hydrogen gas balloons ; and common linen, lined within and without with paper, varnished, for those of rarefied air. Varnished paper, or gold-beaters' skin, will answer the purpose for making small hydrogen gas balloons ; and the small rarefied air bal loons may be made of paper, without any varnish or other preparation. The stuff for large balloons of both kinds requires some previous preparation. The best mode of preparingthe cloth for amachine, upon Montgolfier's principle, is, first to soak it in a solution of sal-ammoniac and size, using one pound of each. to every gallon of water; and when the cloth is quite dry, to paint it over with some earthy colour, and strong size or glue. It may be also varnished over, when per fectly dry, with some stiff; oily varnish, or simple drying linseed oil, which would dry before it penetrates quite through the cloth. The pieces of which an hydrogen gas balloon is to be formed must be cut of aproper size, according to the proposed dimensions of it, when the varnish IS suf ficiently dry. The pieces that compose the surface of the balloon are like those gores that form the superficies of a globe ; and the best method of cutting then is, to describe a pattern of wood or stiff card paper, and to cut the silk or stuff upon it. To the upper part of the balloon there must be adapted a valve, opening inward, to which is annexed a string passing through a hole made in a small round piece of wood, which is fastened to the lowest part of the balloon, opposite to the valve, to the boat below it ; so that the aeronaut may open it as occasion requires, and let the hydrogen gas out of the bal loon. To the lower part of the balloon are fixed two pipes of the same stuff with the covering, six inches in diameter for a balloon of 30 feet, and much larger for balloons of greater size, and long enough to reach the boat. These pipes are the apertures through which the hydrogen gas is introduced into the balloon. The boat may be made of wicker work, and covered with leather, well painted or var nished over. The best method of sus pending it is by means of ropes, proceed ing from the net which goes over the bal loon. This net should be formed to the shape of the balloon, and fall down to the middle of it, and have various cords pro ceeding from it to the circumference of a circle, about two feet below the balloon ; and from that circle other ropes should go to the edge of the boat. This circle may be made of wood, or of several pieces of slen der cane bound together. The meshes of the net may be small at top, against which part of the balloon the hydrogen gas ex erts the greatest force, and increase in size as they recede from the top. A hoop has been sometimes put round the middle of the balloon for fastening the net. This is not absolutely necessary ; but when used, it is best made of pieces of cane bound together, and covered with leather. When the balloon and its appendages are constructed, the next object ofimportfmce is to procure proper materials for filling it. Hydrogen gas for balloons may he obtain ed in several ways; but the best methoas are by applying acids to certain metals by exposing animal, vegetable, and some mineral substances, in a close vessel, to a strong fire ; or by transmitting the va pour of certain fluids through red hot tubes. In the first of these methods, iron,
zinc, and sulphuric acid, are the materials most commonly used. The acid must be diluted with five or six parts of water. Iron may be expected to yield in the common way about 1700 times its own bulk of gas, or 43 ounces of iron ; the like weight of sulphuric acid, and 223 ounces of water, will produce one cubic foot of hydrogen gas ; 6 ounces of zinc, an equal weight of acid, and 30 ounces of water, are necessary for producing the same quantity. It is more proper to use the turnings or chippings of great pieces of iron, as of cannon, &c. than the filings of that metal, because the heat attending the effervescence will be diminished, and the diluted a.cid will pass more readily through the ,interstices of the turnings, when they are heaped together, than through the filings, which stick closer to one another. The weight of the hydro gen gas thus obtained by means of sul phuric acid is, in the common way of procuring it, g-enerally one-seventh part of the weight of common air; and with the necessary precautions for philosophical experiments, less than one-tenth of the weight of common air. We shall con clude this article with a description of some figures explanatory of the subject. Figure 1 (plate Aerostation) rep resents a balloon, DF, suspended by means of the poles G and H, and the cord, for the pur pose of being filled with gas. It is kept steady and held down whilst filling by ropes, which are readily disengaged. A, A, are two tubs, about three feet in diam eter, and two feet deep, inverted in larger tubs, B, B, full of water. At the bottom ofeach ofthe invertedtubes there is a hole, in which is inserted a tin tube ; to these the silken tubes of the balloon are tied. Each of the tubs, 13, is surrounded by se veral strong casks, so regulated in num ber and capacity, as to be less than half full when the materials are equally distri buted. In the top of these casks there are two holes ; to one of which is adapted a tin tube, formed so as to pass over the edg-e of the tub B, ancl through the water, ana to terminate with its aperture under the inverted tub A. The other hole, which serves for supplying the cask with materials, is stopped with a wooden plug. When the balloon is to be filled, the com mon air is first to be expelled, then the silken tubes are fastened round the tin ones ; the iron filings are to be put into the casks, then the water, and lastly the sulphuric acid. The balloon will speedi ly be inflated by the gas, and support it self without the aid of the rope As the filling advances, a net is adjusted about it, the cords proceeding from the net are fastened to the hoop MN ; the boat II( is suspended from the hoop, and whatever is wanted for the voyage is de posited in the boat. M'hen the balloon is sufficienUy full, the silken tubes are sepa rated from the tin tubes, their extremities are tied, and they are placed in the boat. When the aeronauts are seated in the boat, the ropes that held the balloon down are slipped off, and the machine ascends in the air, as in figure 2. ih fig. 3, is a representation of a part of Mr. Garnerin's balloon in its ascent, to which is attached a parachute, in its contracted state, and below is the car. Figure 4 shews the manner in which Mr. Garnerin descended in the car by means of the expanded para chute, after lie had detached it from the balloon. In figure 5 is represented an ap paratus, as described by Mr. Cavallo, for filling- balloons of' the size of two or three feet in diameter with hydrogen gas, after passing it through water. A is a bottle, with the ingredients ; BCD a tube fasten ed in the neck at B, and passing:through C, the cork of the other bottle, in which there is a hole made to receive the tube, and to this the balloon is tied. Thus the hydrogen gas, coming out of the tube D, will pass first through the water of the bottle E, and then into thc balloon. Two small casks may be used instead of the bottles A and E.